Waves from Hurricane Sandy lashed the coast in Scituate last month. Half the world lives within 120 miles of the sea,

By Christina Thompson November 24, 2012

Over the past two and a half million years there have been dramatic changes in the level of the sea. At the end of the last interglacial period, about 10,000 years ago, the ocean was 400 feet lower than it is today, and as we are finally beginning to take in, the sea level is still rising. “[I]nundations,” writes John R. Gillis, author of “The Human Shore: Seacoasts in History,” “are capable of inducing massive population movements and radical changes in ways of life.” His examples include the Netherlands, swamped in 1170, 1362, 1703, 1916, and 1953; Japan; the Maldives; and, somewhat eerily, Long Island.

It was strange to read this book in the wake of both Hurricane Sandy and the presidential election. Today, half the world’s population lives within 120 miles of the sea, and anyone who watched the election returns and saw the count coming in from the big states — California, New York, Texas, Florida — can grasp how true this is for the United States. More than half the American population now lives within 50 miles of a coast.

This has not always been the case, nor has our attitude toward the shore — or indeed the sea — been static over time. As Gillis reminds us, for centuries Europeans considered the sea a place of chaos and terror, a wilderness filled with implacable beasts — Kraken, Leviathan, Scylla, Charybdis. The shore was likewise a liminal region, useful but not entirely to be trusted, a place of, among other things, constant and unpredictable change.

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Our problem today, writes Gillis, is that we have forgotten the lessons of our earliest ancestors, who understood that coastlines are fickle places and that if we want to live near them we must learn to adapt. He cites numerous examples of peoples whose ways of life exemplify this ideal: Marsh Arabs, who live “amphibiously” on floating islands of reeds; the Austronesian mariners who peopled the Pacific; 17th-century Europeans, who learned from Native Americans where to fish and where to live. Coasts, he argues, move and we must move with them, or at least find better ways of dealing with their fluctuations than by barricading ourselves behind a vast array of concrete breakwaters and jetties.

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“The Human Shore” fits into to a recent trend in “oceanic” histories, and Gillis, a professor of history emeritus at Rutgers University, is also the author of an earlier book called “Islands of the Mind” about the place of islands in the Western imagination. Here, in “The Human Shore,” the scope is even greater — a complete history, as Gillis would have it, of “Homo littoralis.” If there is a weakness to the book, however, it is perhaps in this attempt to rope in the whole world, which leads inevitably to gaps and oversimplifications. Gillis is at his best on his home turf of Europe and the New World, particularly Britain and the United States, where he lives “bicoastally” in Maine and California.

The idea that modern Homo littoralis is in trouble, and not just from the rising sea, is hard to argue with. But there is also some risk of romanticizing the peoples, past and present, who appear to have achieved a sustainable existence on the water’s edge. The Pacific, which is the setting for Tim Flannery’s latest book, “Among the Islands,” is arguably the best place to look for successful oceanic and coastal cultures. But, as anyone who has ever read Flannery before will know, it also contains some of the greatest tests of the sustainability hypothesis.

Flannery is a mammalogist and the author of many books, including a groundbreaking study of human interaction with pristine environments called “The Future Eaters.” He is an expert on what people — of all kinds and from all periods — do to the environments in which they live, how hard they are on the fauna (which they mostly eat) and the flora (which they often burn), and how true this has been for tens of thousands of years. In the Pacific, for example, the original Austronesian colonizers of the islands are now known to have hunted many species of bird to extinction and reduced the size and range of shellfish populations through over-harvesting.

These impacts were, of course, trivial in size compared to the modern devastation wrought by development, logging, habitat destruction, pollution, and overfishing. And in this book, which recounts his early years as a field biologist working in the islands of the western Pacific, Flannery is less concerned with how and why animals disappeared than with whether he can find any hidden relics — the odd blossom bat or spotted cuscus — and what can be done to safeguard what is left of the unique fauna in this region of the world.

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Flannery is a witty, good-humored writer with occasional flashes of lyricism and a seemingly endless supply of funny anecdotes. There is a wild one about George, the field-working taxidermist, who discovers belatedly that the island on which he has been left is actually a leper colony; or Greg, the herpetologist, who inadvertently sets up a photo shoot on the site of the village children’s latrine; or the possibly apocryphal story about the early 20th-century collector whose body was sent back from the field, smoked and crated, along with his specimens. But the point, as with all of Flannery’s books, is actually a serious one.

We cannot protect what is left of the world’s biodiversity, Flannery argues, unless we know what it is. In a very real and practical way, scientific description is the first step toward conservation, since governments and other bodies that make environmental policy need a basis on which to act. At the same time, island species give us an exceptional window on how the evolutionary process works, which should be of interest to all of us, writes Flannery, “for evolution by natural selection is the force that shaped us and all the living world.”

Different as they are in scope and tone, both these books are driven by a single imperative — to aid us in going forward by helping us understand the past, and to enlarge our conception of ourselves by asking us to pay more and better attention to the world in which we live.

The Human Shore: Seacoasts in History

By John R. Gillis

University of Chicago, 241 pp., illustrated, $27.50

Among the Islands: Adventures in the Pacific

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By Tim Flannery

Atlantic Monthly 246 pp., illustrated, $25

Christina Thompson is the author of “Come on Shore and We Will Kill and Eat You All” and the editor of Harvard Review.